A drawing of a prior art DC block junction is shown in FIG. 1. Referring to FIG. 1, a prior art coaxial line junction, which will here be referred to as a single sleeve broadband DC block, may be employed in a microwave circuit when transmission of alternating currents (AC) is to be allowed but transmission of direct currents (DC) is to be prevented and blocked. The junction is used in coaxial cables having an outer conductor that is typically grounded and having an outer dielectric. The inner conductor is severed in two at the DC block forming a first inner conductor and a second inner conductor. For purposes of distinction, the prior art junction is characterized as having a first inner conductor with a protruding core and having a second inner conductor with a protruding sleeve. The core and sleeve interfit together. Between the core and the sleeve is an inner dielectric that separates the first and second inner conductor forming a capacitive DC block at the junction. The core is inserted inside the sleeve. Hence, the two inner conductors capacitively couple together with the core being inserted into the sleeve a distance L that is typically chosen to be one-quarter wavelength (L=λ/4) in order to obtain broadband performance.
At low frequencies, the requirement for a one-quarter wavelength coupling section and small junction length cannot be satisfied without using a high dielectric constant material in the coupling region, and therefore requires a trade-off between large size and relatively high insertion loss. This trade-off is highly undesirable for satellite and other space applications in which minimization of mass and insertion loss are critical. These and other disadvantages are solved or reduced using the invention.